/*
 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */
package java.util;

import java.util.function.LongConsumer;
import java.util.function.LongSupplier;
import java.util.function.Supplier;

/**
 * A container object which may or may not contain a {@code long} value.
 * If a value is present, {@code isPresent()} will return {@code true} and
 * {@code getAsLong()} will return the value.
 *
 * <p>Additional methods that depend on the presence or absence of a contained
 * value are provided, such as {@link #orElse(long) orElse()}
 * (return a default value if value not present) and
 * {@link #ifPresent(java.util.function.LongConsumer) ifPresent()} (execute a block
 * of code if the value is present).
 *
 * <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a>
 * class; use of identity-sensitive operations (including reference equality
 * ({@code ==}), identity hash code, or synchronization) on instances of
 * {@code OptionalLong} may have unpredictable results and should be avoided.
 *
 * @since 1.8
 */
public final class OptionalLong {

  /**
   * Common instance for {@code empty()}.
   */
  private static final OptionalLong EMPTY = new OptionalLong();

  /**
   * If true then the value is present, otherwise indicates no value is present
   */
  private final boolean isPresent;
  private final long value;

  /**
   * Construct an empty instance.
   *
   * @implNote generally only one empty instance, {@link OptionalLong#EMPTY}, should exist per VM.
   */
  private OptionalLong() {
    this.isPresent = false;
    this.value = 0;
  }

  /**
   * Returns an empty {@code OptionalLong} instance.  No value is present for this
   * OptionalLong.
   *
   * @return an empty {@code OptionalLong}.
   * @apiNote Though it may be tempting to do so, avoid testing if an object is empty by comparing
   * with {@code ==} against instances returned by {@code Option.empty()}. There is no guarantee
   * that it is a singleton. Instead, use {@link #isPresent()}.
   */
  public static OptionalLong empty() {
    return EMPTY;
  }

  /**
   * Construct an instance with the value present.
   *
   * @param value the long value to be present
   */
  private OptionalLong(long value) {
    this.isPresent = true;
    this.value = value;
  }

  /**
   * Return an {@code OptionalLong} with the specified value present.
   *
   * @param value the value to be present
   * @return an {@code OptionalLong} with the value present
   */
  public static OptionalLong of(long value) {
    return new OptionalLong(value);
  }

  /**
   * If a value is present in this {@code OptionalLong}, returns the value,
   * otherwise throws {@code NoSuchElementException}.
   *
   * @return the value held by this {@code OptionalLong}
   * @throws NoSuchElementException if there is no value present
   * @see OptionalLong#isPresent()
   */
  public long getAsLong() {
    if (!isPresent) {
      throw new NoSuchElementException("No value present");
    }
    return value;
  }

  /**
   * Return {@code true} if there is a value present, otherwise {@code false}.
   *
   * @return {@code true} if there is a value present, otherwise {@code false}
   */
  public boolean isPresent() {
    return isPresent;
  }

  /**
   * Have the specified consumer accept the value if a value is present,
   * otherwise do nothing.
   *
   * @param consumer block to be executed if a value is present
   * @throws NullPointerException if value is present and {@code consumer} is null
   */
  public void ifPresent(LongConsumer consumer) {
    if (isPresent) {
      consumer.accept(value);
    }
  }

  /**
   * Return the value if present, otherwise return {@code other}.
   *
   * @param other the value to be returned if there is no value present
   * @return the value, if present, otherwise {@code other}
   */
  public long orElse(long other) {
    return isPresent ? value : other;
  }

  /**
   * Return the value if present, otherwise invoke {@code other} and return
   * the result of that invocation.
   *
   * @param other a {@code LongSupplier} whose result is returned if no value is present
   * @return the value if present otherwise the result of {@code other.getAsLong()}
   * @throws NullPointerException if value is not present and {@code other} is null
   */
  public long orElseGet(LongSupplier other) {
    return isPresent ? value : other.getAsLong();
  }

  /**
   * Return the contained value, if present, otherwise throw an exception
   * to be created by the provided supplier.
   *
   * @param <X> Type of the exception to be thrown
   * @param exceptionSupplier The supplier which will return the exception to be thrown
   * @return the present value
   * @throws X if there is no value present
   * @throws NullPointerException if no value is present and {@code exceptionSupplier} is null
   * @apiNote A method reference to the exception constructor with an empty argument list can be
   * used as the supplier. For example, {@code IllegalStateException::new}
   */
  public <X extends Throwable> long orElseThrow(Supplier<X> exceptionSupplier) throws X {
    if (isPresent) {
      return value;
    } else {
      throw exceptionSupplier.get();
    }
  }

  /**
   * Indicates whether some other object is "equal to" this OptionalLong. The
   * other object is considered equal if:
   * <ul>
   * <li>it is also an {@code OptionalLong} and;
   * <li>both instances have no value present or;
   * <li>the present values are "equal to" each other via {@code ==}.
   * </ul>
   *
   * @param obj an object to be tested for equality
   * @return {code true} if the other object is "equal to" this object otherwise {@code false}
   */
  @Override
  public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    }

    if (!(obj instanceof OptionalLong)) {
      return false;
    }

    OptionalLong other = (OptionalLong) obj;
    return (isPresent && other.isPresent)
        ? value == other.value
        : isPresent == other.isPresent;
  }

  /**
   * Returns the hash code value of the present value, if any, or 0 (zero) if
   * no value is present.
   *
   * @return hash code value of the present value or 0 if no value is present
   */
  @Override
  public int hashCode() {
    return isPresent ? Long.hashCode(value) : 0;
  }

  /**
   * {@inheritDoc}
   *
   * Returns a non-empty string representation of this object suitable for
   * debugging. The exact presentation format is unspecified and may vary
   * between implementations and versions.
   *
   * @return the string representation of this instance
   * @implSpec If a value is present the result must include its string representation in the
   * result. Empty and present instances must be unambiguously differentiable.
   */
  @Override
  public String toString() {
    return isPresent
        ? String.format("OptionalLong[%s]", value)
        : "OptionalLong.empty";
  }
}
